Thermionic valve integrating circuit



Jan. 15, 1952 L. E. LAND 2,582,490,

THERMIONIC VALVE INTEGRATING CIRCUIT Filed Aug. 30, 1950 IN V EN TOR.

LEONARD ERNEST LAND BY ATTORNEY Patented Jan. 15, 1952 THERMIONIC VALVE INTEGRATING omcm'r Leonard Ernest Land, Winchmore Hill, London,

England, assignor to The General Electric Company Limited, London, England Application August 30, 1950, Serial No. 182,201 In Great Britain September 2, 1949 This invention relates to thermionic valve integrating circuits, that is thermionic valve circuits adapted to provide an output voltage whose instantaneous rate of change with time is substantially proportional to the magnitude of a voltage or current applied to the input of the circuit.

One known form of thermionic valve integrating circuit comprises a valve having at least an anode, a cathode and a control grid, and having a condenser connected between its anode and control grid. In the initial condition of the circuit, one of the electrodes of the valve is biassed suficiently negatively to prevent the flow of anode current in the valve and the condenser is charged up so that the anode of the valve is positive with respect to its control grid. When a voltage is applied between the control grid and cathode of the valve which tends to make the control grid more positive with respect to the cathode, and the bias is removed so as to allow .anode current to flow in the valve, the condenser will discharge through the anode-cathode path so that the anode potential decreases at a rate which is instantaneously proportional to the magnitude of the current flowing into the condenser. If it is desired to integrate an applied voltage, it is necessary to connect a resistance between the control grid of the valve and the positive terminal of thesource of the voltage to be integrated, so that the current flowing into the condenser is proportional to this voltage. When it is desired to restore the circuit to its initial condition, it is necessary to recharge the condenser, and in certain applications of the circuit it is desirable that this should take place as rapidly as possible.

It is an object of the present invention to provide a thermionic valve integrating circuit of the kind described above, in which the restoration of the circuit to its initial condition may be made very rapid.

According to the present invention, a thermionic valve integrating circuit comprises in combination a first thermionic valve having at least an anode, a cathode and a control grid, the source of voltage or current to be integrated being adapted to be connected between the control grid and cathode of said first valve, a condenser connected between the anode and control grid of said first valve, a second thermionic valve having at least an anode, a cathode and a control grid and having its cathode connected to the cathode of said first valve, a diode valve having its cathode connected to the anode of said first 3 Claims. (Cl. 250--2'7) valve and its anode connected to the anode of said second valve, a constant voltage source having its negative terminal connected to the oathodes of said first and second valves and having its positive terminal connected through a low resistance to the anode of said second valve, means for biassing an electrode of each of said first and second valves so that no anode current can flow in said first and second valves while the circuit is in its initialcondition, means for removing the bias from said electrodes so that anode current can flow in said first and second valves when it is desired to integratea voltage or current, and means for restoring the circuit to its initial condition after the integration of a voltage or current comprising means for biassing an electrode of said second valve so that no anode current can flow in said second valve whereby the condenser is recharged through the diode and the low resistance, the arrangement being such that at no time during the integration of a voltage or current does the anode potential of said second valve exceed the anode potential of said first valve.

Preferably said first valve is a pentode and the means for restoring the circuit to its initial condition includes means for biassing the suppressor grid of the pentode so that no anode current flows in the pentode while the condenser is being recharged.

One use of such an integrating circuit is for producing a linear time base, a constant voltage or current being integrated in this case.

In certain applications, for example in pulse communication systems, it is necessary to produce a time base having a duration of a few microseconds and a recovery time not greater than 10 to 20% of the duration of the time base. In addition a high degree of linearity is required, for example it may be required that the deviation of the time base voltage from a perfectly linear sweep should not exceed 0.1% of the total sweep voltage.

One known circuit which may be used under these circumstances comprises a pentode valve having its anode and control grid connected through resistances to the positive terminal and its cathode connected to the negative terminal of a suitable constant voltage source, a condenser connected between the control grid and the anode of the pentode, and means for maintaining the suppressor grid of the pentode alternately at a potential sufficiently negative with respect to its cathode to prevent the flow of anode current and at cathode potential.

The operation of a circuit of this type is as current.

follows. Assuming that the suppressor grid of the pentode is initially at the negative potential, the anode potential will be equal to the potential (EB say) of the voltage source since no anode current is flowing. At the same time the control grid takes current through the resistance connected to it. This resistance is arranged to have a high value and, since the effective resistance between the control grid and cathode is low while the control grid is taking current, the

control grid potential approximates to the oathode potential and the condenser is charged approximately to the full voltage EB of the source The time base is initiated by switching the suppressor grid to cathode potential. Anode current then starts to now in the pentode, and causes the anode potential to fall, the fall in potential being transferred to the control grid via the condenser, thereby reducing the anode A state of equilibrium is rapidly reached, and thereafter the condenser discharges through the valve and the anode potential falls at an approximately uniform rate. The initial rapid drop in anode potential is approximately equal to the grid base of the pentode. At a time T after the beginning of the linear run-clown, the suppressor grid is switched back to the negative potential and the anode current of the pentode is cut oii. The condenser charges again through the anode resistance and the effective resistance between the control grid and the cathode of the pentode and the anode potential returns exponentially to the value E}; with a time constant equal to R1(C1+CP) where R1 is the value of the anode resistance, C1 is the capacity of the condenser, and CP is the anode capacity of the pentode.

It can be shown that during the linear rundown the anode potential V is given by the expression:

potential, and A being the gain of the stage. If the time base were perfectly linear the anode potential V would be given by the expression V =7cT, and therefore V/V is equal to and the percentage deviation from linearity is thus very nearly equal to 50 V AV 0.

The above expression for the linearity of the run-down is derived on the assumption that the gain A of the stage is constant during the rundown. However, this is not correct since the mutual conductance of the valve is dependent upon the anode current and this changes appreciably during the run-down due to the finite value of the anode resistance. When this variation in the mutual conductance is the main factor in determining the linearity the percentage deviation is approximatelycqual to 100 5A/A where all is the change in the gain of the stage during the run-down.

It will thus be seen that a high degree of linearity requires a large value for the gain A and a small change in A during the run-down,

both conditions necessitating a high value of R1, whilst a short flybacl; time requires small values of both R1 and Cl. Reduction of Cl is of only limited value in attaining a rapid flyback, since the anode capacity C}? of the pentode is also charged through the anode resistance, and therefore represents an irreducible minimum capacity. Hence it will be apparent that the requirements of a high degree of linearity in the time base and a short fiyback time are to some extent mutually incompatible when a circuit of the type described above is used.

It is a further object of the present invention to provide a time base circuit in which these two requirements may simultaneously be fulfilled.

According to a feature of the present invention, a linear time base circuit comprises in combination a pentode valve having its control grid connected through a high resistance to a positive terminal and its cathode connected to the negative terminal of a constant voltage source, a condenser connected between the anode and control grid of the pentode, a second thermionic valve having at least a cathode, an anode and a control grid and having its anode connected through a relatively low resistance to a positive terminal of said source and its cathode connected to the cathode of the pentode, a diode valve having its cathode connected to the anode of the pentode and its anode connected to the anode of said second valve, and means for simultaneously maintaining the suppressor grid of the pentode and an electrode of said second valve alternately at potentials sufficient- 1y negative with respect to said negative terminal to prevent the flow of anode current in both the pentode and said second valve and at cathode potential, the arrangement being such that at no time while anode current flows in both the pentode and said second valve does the anode potential of said second valve exceed the anode potential of the pentode.

One arrangement in accordance with the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing which shows a linear time base circuit, incorporating a pentode and a triode.

Referring to the drawing the pentode valve i has its control grid connected through a high resistance 2 to the positive terminal of a suitable constant voltage source 3 and its cathode connected to the negative terminal of the source 3. A condenser 4 is connected between the anode and control grid of the pentode l. The triode 5 has its anode connected through a relatively low resistance *0 to the positive terminal of the source 3 and its cathode connected to the negative terminal of the source S. The anodes of the pentode i and triode 5 are respectively connected to the cathode and anode of a diode I. The screen grid of the pentode l is connected in conventional manner to a point 6 at a suitable potential positive with respect to the oathode, and the suppressor grid of the pentcde l is connected to the grid of the triode 5 and through a resistance 9 to the negative terminal of the source 3. A second constant voltage source ID is provided having its positive terminal connected to the negative terminal of the source 3 and its negative terminal connectable via a suitable switching means H to the suppressor grid of the pentode l and the grid of the triode 5, the magnitude of the voltage produced by the source I0 being sufficient to prevent the flow of anode current in both the triode 5 and the pentode I when the negative terminal of the source I0 is connected to the suppressor grid of the pentode I and the grid of the triode 5. The output from the circuit is taken between the anode and cathode of the pentode I.

The operation of the circuit is as follows. Assuming that the suppressor grid of the pentode I and the grid of the triode 5 are initially at the negative potential, the anode potential of both the triode 5 and the pentode I will be equal to the potential of the source 3, and the condenser will, as in the known arrangement described above, be charged approximately to the full voltage of the source 3.

The time base is initiated by switching the suppressor grid of the pentode I and the grid of the triode 5 to cathode potential. The anode potential of the triode 5 falls rapidly to a steady value while'the anode potential of the pentode I rapidly drops by a small amount initially and then continues with the linear run-down. The arrangement is made such that the value of the anode potential of the pentode is greater throughout the duration of the run-down than the steady anode potential of the triode 5, so that the diode I does not conduct during this period.

At the end of the run-down the suppressor grid of the pentode I and the grid of the triode 5 5 are switched back to the negative potential and the anode currents of both the triode 5 and the pentode I are cut off. The anode potential of the triode 5 then rises rapidly with a time constant equal to R2 CT, where R: is the value of the resistance 6 and CT is the anode capacity of the triode 5, until it reaches a value equal to the anode potential of the pentode I at the end of the linear run-down. At this point the diode begins to conduct and, since the conduction resistance of the diode I is small, the anode potentials of the triode 5 and the pentode I remain approximately equal. The anode potentials of both the triode 5 and the pentode I continue to rise with a time constant approximately equal to R2 (C'T+C'P+C1) where CP is the anode capacity of the pentode I and C1 is the capacity of the condenser l.

Since the value of R2 does not affect the linearity of the run-down, it may be made comparatively small, the limiting factor being the permissible anode current of the triode 5, and the fiyback may therefore be made very fast.

At the same time, the gain A of the stage including the pentode I is equal to the amplification factor of the pentode I and may be of the order of 2,000 as compared with a maximum value of the order of 200 attainable with the known circuit described above. The deviation from linearity due to the finite value of A i therefore much reduced and, since the anode current of the pentode I remains almost perfectly constant during the run-down, the value of A remains almost unchanged during this period.

I claim:

1. A thermionic valve integrating circuit comprising a first thermionic valve having at least an anode, a cathode and a control grid, means for connecting a source of current to be integrated between the control grid and cathode of said first valve, a condenser connected between the anode and control grid of said first valve, a second thermionic valve having at least an anode, a

cathode and a control grid and having its cathode connected to the cathode of said first valve, a diode valve having its cathode connected to the anode of said first valve and its anode connected to the anode of said second valve, a constant voltage source having its negative terminal connected to the cathodes of said first and second valves, a low resistance connected between the positive terminal of the constant voltage source and the anode of said second valve, means for biassing an electrode of each of said first and second valves so that no anode current can flow in said first and second valves while the circuit is in its initial condition, means for removing the bias from said electrodes so that anode current can ilow in said first and second valves when it is desired to integrate a current, and means for restoring the circuit to its initial condition after the integration of a current comprising means for biassing an electrode of said second valve so that no anode current can flow in said second valve whereby the condenser is recharged through the diode and the low resistance, the circuit parameters being such that at no time during the integration of a current does the anode potential of said second valve exceed the anode potential of said first valve.

2. A thermionic valve integrating circuit according to claim 1, in which said first valve is a pentode and the means for restoring the circuit to its initial condition includes means for biassing the suppressor grid of the pentode so that no anode current can flow in the pentode while the condenser is being recharged.

3. A linear time base circuit comprising a pentode valve, a constant voltage source having its negative terminal connected to the cathode of the pentode, a high resistance connected between the control grid of the pentode and a, positive terminal of the constant voltage source, a condenser connected between. the anode and control grid of the pentode, a second thermionic valve having at least a cathode, an anode and a control grid and having its cathode connected to the cathode of the pentode, a low resistance connected between the anode of said second valve and a positive terminal of the constant voltage source, a diode valve having its cathode connected to the anode of the pentode and its anode connected to the anode of said second valve, and means for simultaneously maintaining the suppressor grid of the pentode and an electrode of said second valve alternately at potentials sufficiently negative with respect to said negative terminal to prevent the fiow of anode current in both the pentode and said second valve and at cathode potential, the circuit parameters being such that at no time while anode current flows in both the pentode and said second valve does the anode potential of said second valve exceed the anode potential of the pentode.

LEONARD ERNEST LAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,141,343 Campbell Dec. 27, 1938 2,412,485 Whiteley Dec. 10, 1946 

